Positioning transformer structure



United States Patent C)l 3,263,198 A PGSITIONING TRANSFORMER STRUCT Richard C. Rothweiler, Wauwatosa, Wis., assigner to Square D Company, Park Ridge, Ill., a corporation of Michigan Filed Mar. 27, 1964, Ser. No. 355,243 Claims. (Cl. 336-192) This invention relates rto an air-core .transformer suitable for use in an electrical positioning system, and more particularly to `an elongated primary structure of a positioning transformer havin-g a secondary structure movable axially [along the primary structure to provide a voltage analog of position.

Although having other applications, transformer prir'nary structures in accordance with this invention are ideally suited for use in a positioning system like that of Bulliet et al. Patent No. 2,962,652 which issued on November 29, 1960. Among the problems encountered in the manufacture of such primary stuuctures is the construction of a relatively long coil support or corel which is prefectly straight and which includes means for precisely locating the convolutions of a single turn primary winding disposed therealong. Provision also must be made to connect lead-in wires to accurately spaced taps along the primary winding, and to arrange and hold the lead-in wires in parallel relation to each other in order to minimize inductive effects.

It is an object of this invention to provide an improved primary structure of a positioning transformer.

Another object is to provide a primary structure of a positioning transformer having improved means for joining two elongated coil supports in aligned end-to-end relation.

A further object is to provide ian elongated primary structure of a positioning transformer comprising a coil support with improved means for accurately positioning the convolutions of a winding disposed along its length and for securing lead-in Wires to respective taps spaced along the Winding.

' Other .objects of this invention will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a schematic wiring diagram of a portion of a positioning system using the invention;

FIG. 2 .is an elevational view of a primary structure in vaccordance with .this invention;

FIG. 3 is a View looking at the left-hand end of FIG. 2; FIG. 4 is a view, partially in section, showing the connection of two parts which provide the support for the winding of the primary structure and showing in phantom an arrangement for adjustably positioning the prim-ary structure in FIG. 2 on a support.

FIG. 5 is anenlarged view showing the manner of connection of lead-in wires to a winding wound on the support of FIG. 4.

FIG. 6 is a cross-sectional view taken generally along the line 6 6 ofFIG. 5; and

FIG. 7 shows the primary structure of FIG. 2 including a broken-away portion of the outer covering.

Referring to the schematic wiring diagram of FIG. 1, Y an air-core transformer 10 has a relatively short secondary can be used. The other side L2 of the source 15 is connectible selectively to -a plurality of intermediate taps 12e,

3,263,198 Patented July 26, 1966 "ice 12d, and 12e of the winding 12 by a selector switch 16. It is apparent that the magnitude of the voltage at a pair of terminals 11a and 11b ofthe secondary winding 11 is an analog of the distance between the central portion of the -winding 11 Vand the selected one of the taps 12C, 12d, and

The primary winding 12 schematically shown in FIG. 1

is a part of a primary coil structure 18 illustrated in completed form in FIGS. 2 and 3 land having its details of construction shown in FIGS. 4 through 7.

Referring now principally to FIG. 4, the primary coil struct-ure 18 includes la coil support formed of two tubular cores 19 and 20 which are secured together in axially-aligned, end-to-end relation. T-he cores 19 and 20 are provided with external threads 21 which position the convolutions of the winding 12 as shown in FIG. 7. A plurality of llead-in wires 22 are connected to the winding 12, as will be described. The cores 19 and 20 are preferably formed of laminated vplastic material although other non-magnetic materials, such as 4aluminum and glass, may be used. When used,

y-for example, in a positioning system for a machine tool,

the primary coil structure 18 is generally mounted on a stationary part of the machine and the secondary coil 11 is mounted on a movable part of the machine. For such an application, laminated plastic is the most suitable material for the cores 19 and 20 because it is practically unbreakable, is readily machinable, and can be selected to have a coefficient of thermal expansion which corresponds closely to the coeiiicient of thermal expansion of the metal forming the portion of the machine on whichthe primary coil structure 18 -is mounted.

Because manufacturing capabilities limit the length of tubular cores which may be economically fabricated in one piece, when primary coil structures 18 longer than a few feet are required, it has been found desirable to connect two or more cores, such as the cores 19 and 20, in

end-to-end relation to provide the required over-all length.

As shown in FIG. 4, the left-hand core 19 has a relatively long outer end portion 26 of reduced diameter and an internal annular groove 27 at its other or inner end portion. The other or right-hand core 20 has a relative-` ly short outer end portion 28 of reduced diameter and an internal annular groove 29 at its inner end portion. Each of the coresv 19 and 20 has the threads 21 formed along the entire length thereof except for the reduced end portions 26 and 28. The threads 21 are preferably accurately machined in the cores 19 and 20 to have a predetermined lead which will provide a predetermined number of threads per lineal inch on the cores. ment shown, the threads 21 are machined to provide 20 complete threads per lineal inch. A cylindrical splicing insert 33, having axially spaced annular grooves 34 and 35, is received snugly within the adjacent inner end portions of the cores 19 and 20 with the grooves 34 and 35 radially aligned with the grooves 27 and 29, respectively.` During assembly, the adjacent ends of the cores 19 and 20 are threaded into a nut 36, which is shown in phantom, to force the adjacent end faces of the respectivecores 19 and 20 into intimate contact with each other and to align the threads 21 on lthe respective cores 19 and 20 with one another.

A plurality of openings in the nut are provided which are aligned with respective radial openings 27a and 29a in the cores 19 and 20 so that a suitable bonding material, such as an epoxy resin, can be introduced into the annular space delined by the aligned grooves 27, 29, 34,

In the embodiand 3S. Although only one group of openings 27a and 29a are shown, it will be understood that there may be additional groups of similar openings spaced circumferentially of the group shown. After the resin has solidiied, the nut 36 is removed and the cores 19 and 20 are held securely together in end-to-end 4relation by the bonding material and .the insert 33.

Although the tubes 19 and 20 may be threaded to have any suitable number of threads per inch, twenty threads per inch has been found to be suitable for transformers used in positioning systems for machine tools.

After the cores 19 and 20 are joined together, a series of radial -openings 38 are drilled in the bottom of respective ones of the threads at one inch intervals. The openings 38 are located by drilling a first opening 38a at the bottom of a thread adjacent the reduced end portion 26 of the core 19, and then drilling the remaining openings 38 at spaced intervals of twenty threadsaxially of the cores 19 and 20 and in circumferential alignment with the opening 38a.

The winding 12 is formed by positioning one end portion of a wire 39 over the opening 38a and inserting a U-shaped pin 40 formed from tlat, resilient metal stock over the end portion of the wire 39 and into the opening 38a. The pin 40 and the end portion of the wire 39 are then soldered together. The legs of 'the pin 40 tit snugly into the opening 38a and the resiliency of the pin holds the pin in position and thus holds the wire 39 securely to the core 19. The wire 39 is then wound under constant tension in the valleys of the threads 21. When the wire 39 is positioned to cover the :twentieth thread at each of the openings 38, pieces of sheet insulation 41 are positioned in the twentieth thread at each location -and a pin 40 is positioned in the opening 38 in the twentieth thread, as shown in FIG. 6.

After the entire coil 12 Ihas been wound and the pieces of insulation 41 and pins 40 have been properly positioned, a solderedconnection between the Wire 39 and the one of lthe pins 40 in the final opening 38 adjacent pins 40 andthe wire 39 and a soldered connection is rnade between each of the lead wires 22, the wire 39, and each associated pin 40. The assembly is now as shown at the left in FIG. 7.

As shown at the right in FIG. 7, the lead wires 22 are progressively positioned axially of the core in peripherally disposed relation to each other andare held in position by spaced strips of tape 42. The entire Astructure is then covered with a relatively heavy coating 43 of a suitable resin, such as an epoxy resin. The outer end portions of groups of the lead Wires 22 are connected respectively to suitable terminal blocks 44, as illustrated in FIG. 2.

For mounting the primary structure 18 adjustably on a machine base, a tubular insert 45 is received in the outer end portion 28 of the core 20 and is held in position by a retaining pin 46. The insert 45 has a threaded axial opening which may adjustably receive a threaded arm 48 of a pedestal 49 of a machine base. The other end portion 26 of the core 18 may be slidably supported in a suitable bearing block 50 carried by the machine base.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limitedthereto, as many variations will be'lreadily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims:

What is claimed is:

1. A primary structure of an air-core positioning transformer, said structure comprising a pair of cylindrical cores in axially-aligned, end-to-end engagement with each other, annular grooves in the inner walls of the cores,

respectively, said grooves being positioned near the adjacent ends of the respective cores, a plug having a pair of spaced annular grooves and received in the adjacent end portions of the cores with the grooves in the plug aligned with the grooves in the cores, respectively, bonding material in the spaces defined by the aligned grooves for maintaining the cores and the plug assembled and threads formed on the outer surfaces of each of the cores extending continuously throughout most of their combined length including the adjacent ends, and a winding of conductive Wire in said threads.

2. A primary structure of an air-core positioning transformer, said structure comprising: an externally-threaded elongated tube, a wire wound in the threads to form a primary winding, a plurality of insulated-covered lead-in wires each having a bared end electrically connected to the Wire of the primary winding at a precisely located junction lon the primary winding and each extending from its junction axially along the external surfaces of the tube and primary winding to a terminal end which is disposed beyond one of the ends of the tube, means positioned between the bared ends of thelead wires and the wire of the primary winding in the threads adjacent the junction for insulating the bared end from the wire in said adjacent threads and an insulating covering for said lead-in wires and primary winding for enclosing the primary winding and maintaining the position of the lead-in wires on the tube.

3. A primary structure in accordance with claim 1 characterized in that said'cores have radially-directed holes located at the bottom of selected ones of said threads, respectively, said holes pass through the wall of their associated one of the cores, and U-shaped pins are received in said holes, respectively, each with its bight portion surrounding the wire of said winding overlying its associated one of the holes.

4. A primary structure in accordance with claim 3 characterized in that lead-in wires have end-portions received within the bight portions of some of said pins, respectively, and there are soldered connections between associated ones of `said pins and lead-in wires and between said pins and the wire of said winding.

5. A primary structure of an air-core positioning transformer, said structure comprising an externally-threaded, elongated, cylindrical tube formed of insulating material, a wire wound in the threads to form a primary winding, holes extending through the wall of said tube at spaced intervals axially of the tube and ,opening into the base of selected ones of said threads, respectively, U-shaped pins received in said holes, respectively, with their bight portions surrounding said wire in the region of their associated hole-s, lead-in wires each having an end received within the bight portions of said pins, respectively, and soldered connections between said pins and said ends of the lead-in wires, respectively, and between said pins and the wire of said winding.

References Cited by the Examiner UNITED STATES PATENTS 339,036 3/1886 Wilbur 285-294 1,585,347 5/1926 Heslar 338-303 X 2,368,503 l/l945 Unger 336-192 X 2,406,383 8/ 1946 Kindermann 339-276 2,527,026 12`/l950 Mueller 338-323 2,889,523 6/1959 Henderson 336-83 X 2,925,571 2/1960 Wiegard 336-198 X FOREIGN PATENTS 688,923 3/ 1953 Great Britain.

LARAMIE E. ASKIN, Primary Examiner.

ROBERT K. SCHAFFER, Examiner.

T. I. KOZMA, Assistant Examiner. 

5. A PRIMARY STRUCTURE OF AN AIR-CORE POSITIONING TRANSFORMER, SAID STRUCTURE COMPRISING AN EXTERNALLY-THREADED, ELONGATED, CYLINDRICAL TUBE FORMED ON INSULATING MATERIAL, A WIRE WOUBD IN THREADS TO FORM A PRIMARY WINDING, HOLES EXTENDING THROUGH THE WALL OF SAID TUBE AT SPACED INTERVALS AXIALLY OF THE TUBE AND OPENING INTO THE BASE OF SELECTED ONES OF SAID THREADS, RESPECTIVELY, U-SHAPED PINS RECEIVED IN SAID HOLES, RESPECTIVELY, WITH THEIR BIGHT PORTIONS SURROUNDING SAID WIRES IN THE REGION OF THEIR ASSOCIATED HOLES, LEAD-IN WIRES EACH HAVING AN END RECEIVED WITHIN THE BIGHT PORTIONS OF SAID PINS, RESPECTIVELY, AND SOLDERED CONNECTIONS BETWEEN SAID PINS AND SAID ENDS OF THE LEAD-IN WIRES, RESPECTIVELY, AND BETWEEN SAID PINS AND THE WIRE OF SAID WINDING. 